Resource allocation for shared signaling channels

ABSTRACT

A shared signaling channel can be used in an Orthogonal Frequency Division Multiple Access (OFDMA) communication system to provide signaling, acknowledgement, and power control messages to access terminals within the system. The shared signaling channel may comprise reserved logical resources that can be assigned to subcarriers, OFDM symbols, or combinations thereof.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application claims priority to U.S. patent application Ser.No. 11/261,158 entitled “SHARED SIGNALING CHANNEL,” filed on Oct. 27,2005, which is hereby expressly incorporated by reference herein.

BACKGROUND

1. Field of the Disclosure

The disclosure relates to the field of wireless communications. Moreparticularly, the disclosure relates to resources allocation for ashared signaling channel in a wireless communication system.

2. Description of Related Art

Wireless communication systems can be configured as multiple accesscommunication systems. In such systems, the communication system canconcurrently support multiple users across a predefined set ofresources. Communication devices can establish a link in thecommunication system by requesting access and receiving an access grant.

The resources the wireless communication system grants to the requestingcommunication device depends, largely, on the type of multiple accesssystem implemented. For example, multiple access systems can allocateresources on the basis of time, frequency, code space, or somecombination of factors.

The wireless communication system needs to communicate the allocatedresources and track them to ensure that two or more communicationdevices are not allocated overlapping resources, such that thecommunication links to the communication devices are not degraded.Additionally, the wireless communication system needs to track theallocated resources in order to track the resources that are released orotherwise available when a communication link is terminated.

The wireless communication system typically allocates resources tocommunication devices and the corresponding communication links in acentralized manner, such as from a centralized communication device. Theresources allocated, and in some cases de-allocated, need to becommunicated to the communication devices. Typically, the wirelesscommunication system dedicates one or more communication channels forthe transmission of the resource allocation and associated overhead.

However, the amount of resources allocated to the overhead channelstypically detracts from the resources and corresponding capacity of thewireless communication system. Resource allocation is an importantaspect of the communication system and care needs to be taken to ensurethat the channels allocated to resource allocation are robust. However,the wireless communication system needs to balance the need for a robustresource allocation channel with the need to minimize the adverseeffects on the communication channels.

It is desirable to configure resource allocation channels that providerobust communications, yet introduce minimal degradation of systemperformance.

BRIEF SUMMARY

A shared signaling channel can be used in a wireless communicationsystem to provide signaling messages to access terminals within thesystem. The shared signaling channel can be assigned to a predeterminednumber of sub-carriers within any frame. The assignment of apredetermined number of sub-carriers to the shared signaling channelestablishes a fixed bandwidth overhead for the channel. The actualsub-carriers assigned to the channel can be varied periodically, and canvary according to a predetermined frequency hopping schedule. The amountof signal power allocated to the signaling channel can vary on a persymbol basis depending on the power requirements of the communicationlink. The shared signaling channel can direct each message carried onthe channel to one or more access terminals. Unicast or otherwisedirected messages allow the channel power to be controlled per the needsof individual communication links.

The disclosure includes a method of generating control channel messagesin a wireless communication system. The method comprises assigninglogical control channel resources to physical channel resources, whereinthe logical control channel resources are distinct from logical trafficchannel resources assigned for data transmission and the physicalchannel resources correspond to combinations of sub-carriers and OFDMsymbols. The method also comprises generating and encoding the at leastone message, and then transmitting the at least one message on at leasta portion of the physical channel resources. The above method may alsobe embodied in separate means structures.

The disclosure also includes apparatus configured to generate signalingchannel messages comprising a scheduler configured to assign logicalsignaling channel resources to physical channel resources, wherein thelogical control channel resources are distinct from logical trafficchannel resources assigned to traffic channels that are assigned fordata transmission and the physical channel resources correspond tocombinations of sub-carriers and OFDM symbols. The apparatus alsoincludes a signaling module configured to generate at least onesignaling message and a transmitter configured to transmit the at leastone signaling message utilizing at least some of the subcarriers andOFDM symbols that are assigned to the logical signaling channelresources.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of aspects of the disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings, in which like elements bear likereference numerals.

FIG. 1 is a simplified functional block diagram of aspects of acommunication system having a shared signaling channel.

FIG. 2 is a simplified functional block diagram of aspects of atransmitter supporting a shared signaling channel.

FIG. 3 is a simplified time-frequency diagram of aspects of a sharedsignaling channel.

FIG. 4 illustrates aspects of a method of generating signaling messagesin a communication system with a shared signaling channel.

FIG. 5 illustrates aspects of another method of generating signalingmessages in a communication system with a shared signaling channel.

FIG. 6 illustrates aspects of a simplified apparatus for generatingsignaling messages in a communication system with a shared signalingchannel.

DETAILED DESCRIPTION

A shared signaling channel (SSCH) in an OFDMA wireless communicationsystem can be used to communicate various signaling and feedbackmessages implemented within the system. The wireless communicationsystem can implement a SSCH as one of a plurality of forward linkcommunication channels. The SSCH can be simultaneously or concurrentlyshared among a plurality of access terminals within the communicationsystem.

The wireless communication system can communicate various signalingmessages in a forward link SSCH. For example, the wireless communicationsystem can include access grant messages, forward link assignmentmessages, reverse link assignment messages, as well as any othersignaling messages that may be communicated on a forward link channel.

The SSCH can also be used to communicate feedback messages to accessterminals. The feedback messages can include acknowledgement (ACK)messages confirming successful receipt of access terminal transmissions.The feedback messages can also include reverse link power controlmessages that are used to instruct a transmitting access terminal tovary the transmit power.

The actual channels utilized in an SSCH may be all or some of the onesdescribed above. Additionally, other channels may be included in SSCH inaddition or in lieu of, any of the above channels.

The wireless communication system can allocate a predetermined number ofsub-carriers, OFDM symbols, or combinations thereof to the SSCH.Assigning a predetermined number of sub-carriers, OFDM symbols, orcombinations thereof to the SSCH establishes a bandwidth overhead forthe channel. The actual sub-carriers, OFDM symbols, or combinationsthereof assigned to the SSCH can be varied periodically, and can varyaccording to a predetermined frequency hopping schedule. In certainaspects, the identity of the sub-carriers, OFDM symbols, or combinationsthereof assigned to the SSCH can vary across each frame.

The amount of power that is allocated to the SSCH can vary depending onthe requirements of the communication link carrying the SSCH message.For example, the SSCH power can be increased when the SSCH messages aretransmitted to a distant access terminal. Conversely, the SSCH power canbe decreased when the SSCH messages are transmitted to a nearby accessterminal. If there is no SSCH message to be transmitted, the SSCH neednot be allocated any power. Because the power allocated to the SSCH canbe varied on a per user basis when unicast messaging is implemented, theSSCH requires a relatively low power overhead. The power allocated tothe SSCH increases only as needed by the particular communication link.

The amount of interference that the SSCH contributes to the datachannels for the various access terminals can vary based on thesub-carriers assigned to the SSCH and the access terminals, as well asthe relative power levels of the SSCH and the data channels. The SSCHcontributes substantially no interference for many communication links.

FIG. 1 is a simplified functional block diagram of aspects of a wirelesscommunication system 100 implementing a SSCH on the forward link. Thesystem 100 includes one or more fixed elements that can be incommunication with one or more access terminals 110 a-110 b. Althoughthe description of the system 100 of FIG. 1 generally describes awireless telephone system or a wireless data communication system, thesystem 100 is not limited to implementation as a wireless telephonesystem or a wireless data communication system nor is the system 100limited to having the particular elements shown in FIG. 1.

An access terminal 110 a typically communicates with one or more basestations 120 a or 120 b, here depicted as sectored cellular towers.Other aspects of the system 100 may include access points in place ofthe base stations 120 a and 120 b. In such a system 100, the BSC 130 andMSC 140 may be omitted and may be replaced with one or more switches,hubs, or routers.

As used herein, a base station may be a fixed station used forcommunicating with the terminals and may also be referred to as, andinclude some or all the functionality of, an access point, a Node B, orsome other terminology. An access terminal may also be referred to as,and include some or all the functionality of, a user equipment (UE), awireless communication device, terminal, a mobile station or some otherterminology.

The access terminal 110 a will typically communicate with the basestation, for example 120 b that provides the strongest signal strengthat a receiver within the access terminal 110 a. A second access terminal110 b can also be configured to communicate with the same base station120 b. However, the second access terminal 110 b may be distant from thebase station 120 b, and may be on the edge of a coverage area served bythe base station 120 b.

The one or more base stations 120 a-120 b can be configured to schedulethe channel resources used in the forward link, reverse link, or bothlinks. Each base station, 120 a-120 b, can communicate sub-carrierassignments, acknowledgement messages, reverse link power controlmessages, and other overhead messages using the SSCH.

Each of the base stations 120 a and 120 b can be coupled to a BaseStation Controller (BSC) 140 that routes the communication signals toand from the appropriate base stations 120 a and 120 b. The BSC 140 iscoupled to a Mobile Switching Center (MSC) 150 that can be configured tooperate as an interface between the access terminals 110 a-110 b and aPublic Switched Telephone Network (PSTN) 150. In other aspects, thesystem 100 can implement a Packet Data Serving Node (PDSN) in place orin addition to the PSTN 150. The PDSN can operate to interface a packetswitched network, such as network 160, with the wireless portion of thesystem 100. In certain aspects, system 150 need not utilize a PSTN 150and the MSC 140 may be coupled to the network 160 directly. Inadditional aspects, both the MSC 140 and PSTN 150 may be omitted and BSC130 and/or base stations 120 may coupled directly to a packet based orcircuit switched network 160.

The MSC 150 can also be configured to operate as an interface betweenthe access terminals 110 a-110 b and a network 160. The network 160 canbe, for example, a Local Area Network (LAN) or a Wide Area Network(WAN). In certain aspects, the network 160 includes the Internet.Therefore, the MSC 150 is coupled to the PSTN 150 and network 160. TheMSC 150 can also be configured to coordinate inter-system handoffs withother communication systems (not shown).

The wireless communication system 100 can be configured as an OFDMAsystem with communications in both the forward link and reverse linkutilizing OFDM communications. The term forward link refers to thecommunication link from the base stations 120 a or 120 b to the accessterminals 110 a-110 b, and the term reverse link refers to thecommunication link from the access terminals 110 a-110 b to the basestations 120 a or 120 b. Both the base stations 120 a and 120 b and theaccess terminals 110 a-110 b may allocate resources for channel andinterference estimation.

The base stations, 120 a and 120 b, and the access terminal 110 can beconfigured to broadcast a pilot signal for purposes of channel andinterference estimation. The pilot signal can include broadband pilots,a collection of narrow band pilots that span the overall spectrum, orcombinations thereof.

The wireless communication system 100 can include a set of sub-carriers,alternatively referred to as tones that span an operating bandwidth ofthe OFDMA system. Typically, the sub-carriers are equally spaced. Thewireless communication system 100 may allocate one or more sub-carriersas guard bands, and the system 100 may not utilize the sub-carrierswithin the guard bands for communications with the access terminals 110a-110 b.

In certain aspects, the wireless communication system 100 can include2048 sub-carriers spanning an operating frequency band of 20 MHz, whichmay be divided into independent carriers each housing a fixed portion ofthe 20 MHz with its own SSCH and other resources. A guard band having abandwidth substantially equal to the bandwidth occupied by one or moresub-carriers can be allocated on each end of the operating band.

The wireless communication system 100 can be configured to FrequencyDivision Duplex (FDD) the forward and reverse links. In a FDD aspect,the forward link is frequency offset from the reverse link. Therefore,forward link sub-carriers are frequency offset from the reverse linksub-carriers. Typically, the frequency offset is fixed, such that theforward link channels are separated from the reverse link sub-carriersby a predetermined frequency offset. The forward link and reverse linkmay communicate simultaneously, or concurrently, using FDD.

In another aspect, the wireless communication system 100 can beconfigured to Time Division Duplex (TDD) the forward and reverse links.In such an aspect, the forward link and reverse links can share the samesub-carriers, and the wireless communication system 100 can alternatebetween forward and reverse link communications over predetermined timeintervals. In TDD, the allocated frequency channels are identicalbetween the forward and reverse links, but the times allocated to theforward and reverse links are distinct. A channel estimate performed ona forward or reverse link channel is typically accurate for thecomplementary reverse or forward link channel because of reciprocity.

The wireless communication system 100 can also implement an interlacingformat in one or both the forward and reverse links. Interlacing is aform of time division multiplexing in which the communication linktiming is cyclically assigned to one of a predetermined number ofinterlace periods. A particular communication link to one of the accessterminals, for example 110 a, can be assigned to one of the interlaceperiods, and communications over the particular assigned communicationlink occurs only during the assigned interlace period. For example, thewireless communication system 100 can implement an interlace period ofsix. Each interlace period, identified 1-6, has a predeterminedduration. Each interlace period occur periodically with a period of six.Thus, a communication link assigned to a particular interlace period isactive once every six periods.

Interlaced communications are particularly useful in wirelesscommunication systems 100 implementing an automatic repeat requestarchitecture, such as a Hybrid Automatic Repeat Request (HARQ)algorithm. The wireless communication system 100 can implement a HARQarchitecture to process data retransmission. In such a system, atransmitter may send an initial transmission at a first data rate andmay automatically retransmit the data if no acknowledgement message isreceived. The transmitter can send subsequent retransmissions at lowerdata rates. HARQ incremental redundancy retransmission schemes canimprove system performance in terms of providing early termination gainand robustness.

The interlace format allows sufficient time for processing of the ACKmessages prior to the next occurring assigned interlace period. Forexample, an access terminal 110 acan receive transmitted data andtransmit an acknowledgement message, and a base station 120 b canreceive and process the acknowledgement message in time to preventretransmission at the next occurring interlace period. Alternatively, ifthe base station 120 bfails to receive the ACK message, the base station120 b can retransmit the data at the next occurring interlace periodassigned to the access terminal 110 a.

The base stations 120 a-120 b can transmit the SSCH messages in eachinterlace, but may limit the messages occurring in each interlace tothose messages intended for access terminals 110 a-110 bassigned to thatparticular active interlace. The base stations 120 a-120 bcan limit theamount of SSCH messages that need to be scheduled in each interlaceperiod.

The wireless communication system 100 can implement a Frequency DivisionMultiplex (FDM) SSCH in the forward link for the communication ofsignaling and feedback messages. Each base station 120 a-120 b canallocate a predetermined, or variable, number of sub-carriers, OFDMsymbols, or combinations thereof to the SSCH. In other aspects, onlylogical resources may be assigned to the SSCH and those resources thenmapped according to a mapping scheme, which may be the same or differentas the mapping scheme for traffic channels, The wireless communicationsystem 100 can be configured to allocate a fixed, or variable, bandwidthoverhead to the SSCH. Each base station 120 a-120 b can allocate apredetermined percentage, with a minimum and maximum, of its physicalchannel resources, e.g. sub-carriers, OFDM symbols, or combinationsthereof, to the SSCH. Additionally, each base station 120 a or 120 b mayallocate a different set of physical channel resources to the SSCH. Forexample, each base station 120 a or 120 b can be configured to allocateapproximately 10% of the physical channel resources to the SSCH.

Each base station, for example 120 b, can allocate logical resources inthe form a plurality of nodes from a channel tree to the SSCH. Thechannel tree is a channel model that can include a plurality of branchesthat eventually terminate in leaf or base nodes. Each node in the treecan be labeled, and each node identifies every node and base nodebeneath it. A leaf or base node of the tree can correspond to thesmallest assignable logical resource, such as a single sub-carrier, OFDMsymbol, or a combination of a sub-carrier and OFDM symbol. Thus, thechannel tree provides a logical map for assigning and tracking theavailable physical channel resources in the wireless communicationsystem 100.

The base station 120 b can map the nodes from the channel tree tophysical channel resources used in the forward and reverse links. Forexample, the base station 120 b can allocate a predetermined number ofresources to the SSCH by assigning a corresponding number of base nodesfrom a channel tree to the SSCH. The base station 120 b can map thelogical node assignment to a physical channel resources assignment thatultimately is transmitted by base station 120 b.

It may be advantageous to use the logical channel tree structure or someother logical structure to track the resources assigned to the SSCH whenthe physical channel resource assignments can change. For example, thebase stations 120 a-120 b can implement a frequency hopping algorithmfor the SSCH as well as other channels, such as data channels. The basestations 120 a-120 b can implement a pseudorandom frequency hoppingscheme for each assigned sub-carrier. The base stations 120 a-120 b canuse the frequency hopping algorithm to map the logical nodes from thechannel tree to corresponding physical channel resource assignments.

The frequency hopping algorithm can perform frequency hopping on asymbol basis or a block basis. Symbol rate frequency hopping canfrequency hop each individual sub-carrier distinct from any othersub-carrier, except that no two node are assigned to the same physicalsub-carrier. In block hopping, a contiguous block of sub-carriers can beconfigured to frequency hop in a manner that maintains the contiguousblock structure. In terms of the channel tree, a branch node that ishigher than a leaf node can be assigned to a hopping algorithm. The basenodes under the branch node can follow the hoping algorithm applied tothe branch node.

The base station 120 a-120 b can perform frequency hopping on a periodicbasis, such as each frame, a number of frames, or some otherpredetermined number of OFDM symbols. As used herein, a frame refers toa predetermined structure of OFDM symbols, which may include one or morepreamble symbols and one or more data symbols. The receiver can beconfigured to utilize the same frequency hopping algorithm to determinewhich sub-carriers are assigned to the SSCH or a corresponding datachannel.

The base stations 120 a-120 b can modulate each of the sub-carriersassigned to the SSCH with the SSCH messages. The messages can includesignaling messages and feedback messages. The signaling messages caninclude access grant messages, forward link assignment block messages,and reverse link block assignment messages. The feedback messages caninclude acknowledgement (ACK) messages and reverse link power controlmessages. The actual channels utilized in an SSCH may be all or some ofthe ones described above. Additionally, other channels may be includedin SSCH in addition or in lieu of, any of the above channels.

The access grant message is used by the base station 120 b toacknowledge an access attempt by an access terminal 110 a and assign aMedia Access Control Identification (MACID). The access grant messagecan also include an initial reverse link channel assignment. Thesequence of modulation symbols corresponding to the access grant can bescrambled according to an index of the preceding access probetransmitted by the access terminal 110 a. This scrambling enables theaccess terminal 110 a to respond only to access grant blocks thatcorrespond to the probe sequence that it transmitted.

The base station 120 b can use the forward and reverse link access blockmessages to provide forward or reverse link sub-carrier assignments. Theassignment messages can also include other parameters, such asmodulation format, coding format, and packet format. The base stationtypically provides a channel assignment to a particular access terminal110 a, and can identify the target recipient using an assigned MACID.

The base stations 120 a-120 b typically transmit the ACK messages toparticular access terminals 110 a-110 b in response to successfulreceipt of a transmission. Each ACK message can be as simple as aone-bit message indicating positive or negative acknowledgement. An ACKmessage can be linked to each sub-carrier, e.g. by using related nodesin a channel tree to others for that access terminal, or can be linkedto a particular MACID. Further, the ACK messages may be encoded overmultiple packets for the purposes of diversity.

The base stations 120 a-120 b can transmit reverse link power controlmessages to control the power density of reverse link transmissions fromeach of the access terminals 110 a-110 b. The base station 120 a-120 bcan transmit the reverse power control message to command the accessterminal 110 a-110 b to increase or decrease its power density.

The base stations 120 a-120 b can be configured to unicast each of theSSCH messages individually to particular access terminals 110 a-110 b.In unicast messaging, each message is modulated and power controlledindependently from other messages. Alternatively, messages directed to aparticular user can be combined and independently modulated and powercontrolled.

In another aspect, the base stations 120 a-120 b can be configured tocombine the messages for multiple access terminals 110 a-110 b andmulti-cast the combined message to the multiple access terminals 110a-110 b. In multicast, messages for multiple access terminals can begrouped in jointly encoded and power controlled sets. The power controlfor the jointly encoded messages needs to target the access terminalhaving the worst communication link. Thus, if the messages for twoaccess terminals 110 a and 110 b are combined, the base station 120 bsets the power control of the combined message to ensure that the accessterminal 110 a having the worst link receives the transmission. However,the level of power needed to ensure the worst communication link issatisfied may be substantially greater than required for an accessterminal 110 b at a close proximity to the base station 120 b.Therefore, in some aspects SSCH messages may be jointly encoded andpower controlled for those access terminals having substantially similarchannel characteristics, e.g. SNRs, power offsets, etc.

In another aspect, the base stations 120 a-120 b can group all of themessage information for all access terminals 110 a-110 b served by abase station, for example 120 b, and broadcast the combined message toall of the access terminals 110 a-110 b. In the broadcast approach, eall messages are jointly coded and modulated while power control targetsthe access terminal with the worst forward link signal strength.

Unicast signaling may be advantageous in those situations wheremulticast and broadcast require substantial power overhead to reach celledge for a substantial number of bits. Unicast messages may benefit frompower sharing between access terminals with different forward linksignal strength through power control. Unicast messaging also benefitsfrom the fact that many reverse link base nodes may not be assigned atany given point in time so that no energy needs to be expended reportingan ACK for those nodes.

From the MAC logic standpoint, unicast design enables the wirelesscommunication system 100 to scramble ACK messages with the target MACID,preventing an access terminal that erroneously thinks that it isassigned the relevant resources targeted by the ACK (via assignmentsignaling errors such as missed de-assignment) from falsely interpretingthe ACK that is actually intended for another MACID. Thus, such anaccess terminal will recover from the erroneous assignment state after asingle packet since that packet cannot be positively acknowledged, andthe access terminal will expire the erroneous assignment.

From the link performance standpoint, the main advantage of broadcast ormulticast methods is coding gain due to joint encoding. However, thegain of power control exceeds substantially coding gain for practicalgeometry distributions. Also, unicast messaging can exhibit higher errorrates compared to jointly encoded and CRC protected messages. However,practically achievable error rates of 0.01% to 0.1% are satisfactory.

It may be advantageous for the base stations 120 a-120 b to multicast orbroadcast some messages while unicasting others. For example, anassignment message can be configured to automatically de-assignresources from the access terminal that is currently using resourcescorresponding to the sub-carriers indicated in the assignment message.Hence, assignment messages are often multicast since they target boththe intended recipient of the assignment as well as any current users ofthe resources specified in the assignment message.

FIG. 2 is a simplified functional block diagram of an aspect of an OFDMAtransmitter 200 such as can be incorporated within a base station of thewireless communication system of FIG. 1. The transmitter 200 isconfigured to transmit one or more OFDMA signals to one or more accessterminals. The transmitter 200 includes a SSCH module 230 configured togenerate and implement a SSCH in the forward link.

The transmitter 200 includes a data buffer 210 configured to store datadestined for one or more access terminals. The data buffer 210 can beconfigured, for example, to hold the data destined for each of theaccess terminals in a coverage area supported by the corresponding basestation.

The data can be, for example, raw unencoded data or encoded data.Typically, the data stored in the data buffer 210 is unencoded, and iscoupled to an encoder 212 where it is encoded according to a desiredencoding rate. The encoder 212 can include encoding for error detectionand Forward Error Correction (FEC). The data in the data buffer 210 canbe encoded according to one or more encoding algorithms. Each of theencoding algorithms and resultant coding rates can be associated with aparticular data format of a multiple format Hybrid Automatic RepeatRequest (HARQ) system. The encoding can include, but is not limited to,convolutional coding, block coding, interleaving, direct sequencespreading, cyclic redundancy coding, and the like, or some other coding.

The encoded data to be transmitted is coupled to a serial to parallelconverter and signal mapper 214 that is configured to convert a serialdata stream from the encoder 212 to a plurality of data streams inparallel. The signal mapper 214 can determine the number of sub-carriersand the identity of the sub-carriers for each access terminal based oninput provided by a scheduler (not shown). The number of carriersallocated to any particular access terminal may be a subset of allavailable carriers. Therefore, the signal mapper 214 maps data destinedfor a particular access terminal to those parallel data streamscorresponding to the data carriers allocated to that access terminal.

A SSCH module 230 is configured to generate the SSCH messages, encodethe messages, and provide the encoded messages to the signal mapper 214.The SSCH module 230 can also provide the identity of the sub-carriersassigned to the SSCH. The SSCH module 230 can include a scheduler 252configured to determine and assign nodes from a channel tree to theSSCH. The output of the scheduler 252 can be coupled to a frequencyhopping module 254. The frequency hopping module 254 can be configuredto map the assigned channel tree nodes determined by the scheduler 252to the physical sub-carrier assignments. The frequency hopping module254 can implement a predetermined frequency hopping algorithm.

The signal mapper 214 receives the SSCH message symbols and sub-carrierassignments, and maps the SSCH symbols to the appropriate sub-carriers.In certain aspects, the SSCH module 230 can be configured to generate aserial message stream and the signal mapper 214 can be configured to mapthe serial message to the assigned sub-carriers.

In certain aspects, the signal mapper 214 can be configured tointerleave each modulation symbol from the SSCH message across all ofthe assigned sub-carriers. Interleaving the modulation symbols for theSSCH provides the SSCH signal with the maximum frequency andinterference diversity.

The output of the signal mapper 214 is coupled to a pilot module 220that is configured to allocate a predetermined portion of thesub-carriers to a pilot signal. In certain aspects, the pilot signal caninclude a plurality of equally spaced sub-carriers spanningsubstantially the entire operating band. The pilot module 220 can beconfigured to modulate each of the carriers of the OFDMA system with acorresponding data or pilot signal.

In certain aspects, the SSCH symbols are used to BPSK modulate theassigned sub-carriers. In another aspect, the SSCH symbols are used toQPSK modulate the assigned sub-carriers. While practically anymodulation type can be accommodated, it may be advantageous to use amodulation format that has a constellation that can be represented by arotating phasor, because the magnitude does not vary as a function ofthe symbol. This may be beneficial because SSCH may then have differentoffsets but the same pilot references, and thereby be easier todemodulate.

The output of the pilot module 220 is coupled to an Inverse Fast FourierTransform (IFFT) module 222. The IFFT module 222 is configured totransform the OFDMA carriers to corresponding time domain symbols. Ofcourse, a Fast Fourier Transform (FFT) implementation is not arequirement, and a Discrete Fourier Transform (DFT) or some other typeof transform can be used to generate the time domain symbols. The outputof the IFFT module 222 is coupled to a parallel to serial converter 224that is configured to convert the parallel time domain symbols to aserial stream.

The serial OFDMA symbol stream is coupled from the parallel to serialconverter 224 to a transceiver 240. In the aspect shown in FIG. 2, thetransceiver 240 is a base station transceiver configured to transmit theforward link signals and receive reverse link signals.

The transceiver 240 includes a forward link transmitter module 244 thatis configured to convert the serial symbol stream to an analog signal atan appropriate frequency for broadcast to access terminals via anantenna 246. The transceiver 240 can also include a reverse linkreceiver module 242 that is coupled to the antenna 246 and is configuredto receive the signals transmitted by one or more remote accessterminals.

The SSCH module 230 is configured to generate the SSCH messages. Asdescribed earlier, The SSCH messages can include signaling messages.Additionally, the SSCH messages can include feedback messages, such asACK messages or power control messages. The SSCH module 230 is coupledto the output of the receiver module 242 and analyzes the receivedsignals, in part, to generate the signaling and feedback messages.

The SSCH module 230 includes a signaling module 232, an ACK module 236,and a power control module 238. The signaling module 232 can beconfigured to generate the desired signaling messages and encode themaccording to the desired encoding. For example, the signaling module 232can analyze the received signal for an access request and can generatean access grant message directed to the originating access terminal. Thesignaling module 232 can also generate and encode any forward link orreverse link block assignment messages.

Similarly, the ACK module 236 can generate ACK messages directed toaccess terminals for which a transmission was successfully received. TheACK module 236 can be configured to generate unicast, multicast, orbroadcast messages, depending on the system configuration.

The power control module 238 can be configured to generate any reverselink power control messages based in part on the received signals. Thepower control module 238 can also be configured to generate the desiredpower control messages.

The power control module 238 can also be configured to generate thepower control signals that control the power density of the SSCHmessages. The SSCH module 230 can power control individual unicastmessages based on the needs of the destination access terminal.Additionally, the SSCH module 230 can be configured to power control themulticast or broadcast messages based on the weakest forward link signalstrength reported by the access terminals. The power control module 238can be configured to scale the encoded symbols from each of the moduleswithin the SSCH module 230. In another aspect, the power control module238 can be configured to provide control signals to the pilot module 220to scale the desired SSCH symbols. The power control module 238 thusallows the SSCH module 230 to power control each of the SSCH messagesaccording to its needs. This results in reduced power overhead for theSSCH.

It should be noted that one or more elements depicted in FIG. 2, may beintegrated into a processor with integrated or and external memorymodule.

FIG. 3 is a simplified time-frequency diagram 300 of an aspect of ashared signaling channel, such a channel generated by the SSCH module ofthe transmitter of FIG. 2. The time frequency diagram 300 details theSSCH sub-carrier allocation for two successive frames,310 and 320. Thetwo successive frames 310 and 320 can represent the successive frames ofan FDM system of a TDM system, although the successive frames in a TDMsystem may have one or more intervening frames allocated to reverse linkaccess terminal transmissions (not shown).

The first frame 310 includes three frequency bands,312 a-312 c, that canbe representative of three separate sub-carriers assigned to the SSCH inthe particular frame. The three sub-carrier assignments 312 a-312 c areshown as maintained over the entire duration of the frame 310. In someaspects, the sub-carrier assignments can change during the course of theframe 310. The number of times that the sub-carrier assignments canchange during the course of a frame 310 is defined by the frequencyhopping algorithm, and is typically less than the number of OFDM symbolsin the frame 310.

In the aspect shown in FIG. 3, the sub-carrier assignment changes on theframe boundary. The second, successive frame 320 also includes the samenumber of sub-carriers assigned to the SSCH as in the first frame 310.In certain aspects, the number of sub-carriers assigned to the SSCH ispredetermined and fixed. For example, the SSCH bandwidth overhead can befixed to some predetermined level. In another aspect, the number ofsub-carriers assigned to the SSCH is variable, and can be assigned by asystem control message. Typically, the number of sub-carriers assignedto the SSCH does not vary at a high rate.

The sub-carriers mapped to the SSCH can be determined by a frequencyhopping algorithm that maps a logical node assignment to a physicalsub-carrier assignment. In the aspect shown in FIG. 3, the threesub-carrier physical assignments 322 a-322 c are different in thesecond, successive frame 320. As before, the aspect depicts thesub-carrier assignments as stable for the entire length of the frame320.

It should be noted that while FIG. 3 depicts an SSCH assigned to anumber of contiguous OFDM symbols for one or more subcarriers This neednot be the case and the SSCH may be mapped in any fashion, e.g. in asymbol rate hopping fashion or blocks of adjacent subcarriers, OFDMsymbols, or combinations thereof for one or more symbols. It should benoted that as depicted in FIG. 3, the schemes for allocating resourcesmay be different for data and SSCH channels. Further, in the case thatdata transmissions are assigned to logical control channel resources,those assignments would be dropped, or otherwise not carried out at thebase station.

FIG. 4 illustrates aspects of a method 400 of generating signalingmessages in a communication system with a shared signaling channel. Thetransmitter having the SSCH module as shown in FIG. 2 can be configuredto perform the method 400. The method 400 depicts the generation of oneframe of SSCH messages. The method 400 can be repeated for additionalframes.

The method 400 begins at block 410 where the SSCH module generates thesignaling messages. The SSCH module can generate signaling messages inresponse to requests. For example, the SSCH module can generate accessgrant messages in response to access requests. Similarly, the SSCHmodule can generate forward link or reverse link assignment blockmessages in response to a link request or a request to transmit data.

The SSCH module proceeds to block 412 and encodes the signalingmessages. The SSCH can be configured to generate unicast messages forparticular message types, for example access grants. The SSCH module canbe configured to identify a MACID of a destination access terminal whenformatting a unicast message. The SSCH module can encode the message andcan generate a CRC code and append the CRC to the message. Additionally,the SSCH can be configured to combine the messages for several accessterminals into a single multicast or broadcast message and encode thecombined messages. The SSCH can, for example, include a MACID designatedfor broadcast messages. The SSCH can generate a CRC for the combinedmessage and append the CRC to the encoded messages.

The SSCH module can, though need not, proceed to block 414 to powercontrol the signaling messages. In certain aspects, the SSCH can adjustor otherwise scale the amplitude of the encoded messages. In anotheraspect, the SSCH module can direct a modulator to scale the amplitude ofthe symbols.

The SSCH module then may, though need not, perform similar operationsfor the generation of ACK and reverse link power control feedbackmessages. At block 420, the SSCH module generates the desired ACKmessages based on received access terminal transmissions. The SSCHmodule proceeds to block 420 and encodes the ACK messages, for example,as unicast messages. The SSCH module proceeds to block 424 and adjuststhe power of the ACK symbols.

The SSCH module proceeds to block 430 and generates reverse link powercontrol messages based, for example, on the received signal strength ofeach individual access terminal transmission. The SSCH module proceedsto block 432 and encodes the power control messages, typically asunicast messages. The SSCH module proceeds to block 434 and adjusts thepower of the reverse link power control message symbols.

The SSCH proceeds to block 440 and determines which logical resources,such as a channel tree, are assigned to the SSCH. The SSCH moduleproceeds to block 450 and maps the physical channel resources assignmentto the assigned nodes. The SSCH module can use a frequency hoppingalgorithm to map the logical node assignment to the physical channelresource assignment. The frequency hopping algorithm can be such thatthe same node assignment can produce different physical channelresources assignments for different frames. The frequency hopper canthus provide a level of frequency diversity, as well as some level ofinterference diversity.

The SSCH proceeds to block 460 and maps the message symbols to theassigned physical channel resources. The SSCH module can be configuredto interleave the message symbols among the assigned physical channelresources to introduce diversity to the signal.

The symbols modulate the OFDM sub-carriers, and the modulatedsub-carriers are transformed to OFDM symbols that are transmitted to thevarious access terminals. The SSCH module allows a fixed bandwidth FDMchannel to be used for signaling and feedback messages while allowingflexibility in the amount of power overhead that is dedicated to thechannel.

It should be noted that while FIG. 4 illustrates generating SSCHtransmissions including signaling, acknowledgement, power control, andassignment messages one or more of these, along with one or more othermessage types may be utilized in place of the arrangement described.

FIG. 5 illustrates aspects of another method 500 of generating signalingmessages in a communication system with a shared signaling channel. Themethod 500 may begins at block 510 where logical control channelresources are assigned to physical channel resources. The logicalcontrol channel resources are distinct from logical traffic channelresources assigned to physical channel resources for data transmission.In certain aspects, the distinction may be provided assigning logicalresources only to signaling channel. In other aspects, these resourcesmay be reserved for the signaling channel, but allow the system, e.g.the scheduler, to assign any unused logical resources reserved to thesignaling channel to data transmissions. Further, the logical resourcesmay be nodes of a channel tree, hop ports of a frequency hop algorithm,or other logical resources. In certain aspects, the physical channelresources correspond to sub-carriers, OFDM symbols, or combinations ofsub-carriers and OFDM symbols.

The assignment of the resources may vary according to one or morefrequency hopping algorithms utilized. These hopping algorithms may varyfor the logical resources assigned to signaling and data channels, e.g.different channel trees may be utilized for the logical signalingchannel resources and the logical data channel resources. Further, eachof the different types of signaling channel resources, e.g. signaling,acknowledgement, power control, and assignment, may have distinctlogical resources, or may all be arbitrarily or deterministically mappedto the logical, or physical after assignment, resources assigned to thesignaling resources.

Signaling messages may then be generated, block 520, and encoded, block530. The messages are then transmitted based upon a mapping of symbolscorresponding to the messages to the physical channel resources assignedto the logical signaling channel resources, block 540. Th signalingmessages may be of signaling, acknowledgement, power control,assignment, or other types. Further, a single message may have multiplesignaling message types, e.g. a unicast message may have signaling,acknowledgements, and power control information for a particular user.

Additional, power control of the signaling messages or symbols thereofmay be performed by SSCH module by adjusting or otherwise scale theamplitude of the encoded messages or symbols.

Although FIG. 5 depicts assignment occurring prior to symbol modulationand encoding, the orders of the three functions may be independent, e.g.reversed or contemporaneous, with respect to the three other functions.

It should be noted that in some cases, e.g. where a same channel tree isused for both signaling, e.g. SSCH, logical resources, and data logicalresources, a scheduler may assign a logical resource reserved forsignaling for data channels. In such cases, the logical resource will bedropped from the transmission resources assigned to the terminal.Alternatively, a re-assignment may also be possible, e.g. eachassignment of a logical resource reserved for signaling has one or morerelated logical resources to which data assignments are transferred,when a data channel is assigned to the logical resource reserved forsignaling.

FIG. 6 illustrates aspects of a simplified apparatus 600 for generatingsignaling messages in a communication system with a shared signalingchannel. The apparatus includes means 610 for assigning logical controlchannel resources a to physical channel resources. The logical controlchannel resources are distinct from logical traffic channel resourcesassigned to physical channel resources for data transmission. In certainaspects, the distinction may be provided assigning logical resourcesonly to signaling channel. In other aspects, these resources may bereserved for the signaling channel, but allow the system, e.g. thescheduler, to assign any unused logical resources reserved to thesignaling channel to data transmissions. Further, the logical resourcesmay be nodes of a channel tree, hop ports of a frequency hop algorithm,or other logical resources. In certain aspects, the physical channelresources correspond to sub-carriers, OFDM symbols, or combinations ofsub-carriers and OFDM symbols.

The assignment of the resources may vary according to one or morefrequency hopping algorithms utilized. These hopping algorithms may varyfor the logical resources assigned to signaling and data channels, e.g.different channel trees may be utilized for the logical signalingchannel resources and the logical data channel resources. Further, eachof the different types of signaling channel resources, e.g. signaling,acknowledgement, power control, and assignment, may have distinctlogical resources, or may all be arbitrarily or deterministically mappedto the logical, or physical after assignment, resources assigned to thesignaling resources.

Apparatus 600 includes means 620 for generating signaling messages andmeans 630 for encoding the signaling messages. The messages are thentransmitted based upon a mapping of symbols corresponding to themessages to the physical channel resources assigned to the logicalsignaling channel resources by transmitter 640. Th signaling messagesmay be of signaling, acknowledgement, power control, assignment, orother types. Further, a single message may have multiple signalingmessage types, e.g. a unicast message may have signaling,acknowledgements, and power control information for a particular user.

Additional, power control of the signaling messages or symbols thereofmay be performed by means such as power control module 238.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), a Reduced Instruction Set Computer (RISC) processor, anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A generalpurpose processor may be a microprocessor, but in the alternative, theprocessor may be any processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, for example, a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method, process, or algorithm described in connectionwith the aspects disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo.

A software module may reside in RAM memory, flash memory, non-volatilememory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. Further, the various methods may be performed in theorder shown in the aspects or may be performed using a modified order ofsteps. Additionally, one or more process or method steps may be omittedor one or more process or method steps may be added to the methods andprocesses. An additional step, block, or action may be added in thebeginning, end, or intervening existing elements of the methods andprocesses.

The above description of the disclosed aspects is provided to enable anyperson of ordinary skill in the art to make or use the disclosure.Various modifications to these aspects will be readily apparent to thoseof ordinary skill in the art, and the generic principles defined hereinmay be applied to other aspects without departing from the spirit orscope of the disclosure. Thus, the disclosure is not intended to belimited to the aspects shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

1. A method of generating control channel messages in a wireless communication system, the method comprising: assigning logical control channel resources to physical channel resources to create assigned physical channel resources, wherein the logical control channel resources are distinct from logical traffic channel resources assigned for data transmission and the physical channel resources correspond to combinations of sub-carriers and OFDM symbols; generating at least one message; encoding the at least one message to generate at least one message symbol; and transmitting the at least one message on at least a portion of the assigned physical channel resources.
 2. The method of claim 1, further comprising controlling a power density of the at least one message. transforming the plurality of sub-carriers, including at least one sub-carrier within the assigned physical channel resources, to an OFDM symbol; and transmitting the OFDM symbol over a wireless communication link.
 3. The method of claim 1, wherein assigning comprises assigning based in part on a frequency hopping algorithm.
 4. The method of claim 1, wherein the logical control channel resources comprise nodes of a channel tree and assigning comprises mapping the nodes to a sub-carriers and OFDM symbols.
 5. The method of claim 4, wherein mapping comprises mapping the nodes based in part on a frequency hopping algorithm.
 6. The method of claim 1, wherein the logical control channel resources comprise a number of logical resources that may vary between a minimum and a maximum and wherein assigning comprises selecting a number of logical resources for control channel resources between the minimum and the maximum.
 7. The method of claim 6, further comprising releasing any logical resources between the maximum and the number of selected logical resources for assignment to traffic channels.
 8. The method of claim 1, wherein generating at least one message comprises generating at least one assignment block message directed to a plurality of access terminals.
 9. The method of claim 8, wherein the at least one assignment block message comprises a broadcast MACID.
 10. The method of claim 1, wherein generating at least one message comprises generating at least one acknowledgement (ACK) message in response to a received transmission from an access terminal.
 11. The method of claim 1, wherein generating at least one message comprises generating at least one reverse power link control message directed to a particular access terminal.
 12. The method of claim 1, further comprising determining if at least one logical control channel resource is assigned for data transmission, and if the at least one logical control channel resource is assigned to data, then cancelling the assignment.
 13. An apparatus configured to generate signaling channel messages in a wireless communication system, the apparatus comprising: a scheduler configured to assign logical signaling channel resources to physical channel resources to provide assigned physical channel resources, wherein the logical control channel resources are distinct from logical traffic channel resources assigned to traffic channels that are assigned for data transmission and the physical channel resources correspond to combinations of sub-carriers and OFDM symbols; a signaling module configured to generate at least one signaling message; and a transmitter coupled to the scheduler and the signaling module, the transmitter configured to transmit the at least one signaling message utilizing at least some of the assigned physical channel resources.
 14. The apparatus of claim 13, wherein the scheduler is configured to assign the physical channel resources based in part on a frequency hopping algorithm.
 15. The apparatus of claim 13, wherein the logical control channel resources comprise nodes of a channel tree and wherein the scheduler is configured to map the nodes to sub-carriers and OFDM symbols.
 16. The apparatus of claim 13, wherein the at least one signaling message comprises a broadcast signaling message directed to a plurality of access terminals.
 17. The apparatus of claim 13, wherein the logical control channel resources comprise nodes of a channel tree and a wherein the scheduler is configured to map the nodes to a sub-carriers and OFDM symbols.
 18. The apparatus of claim 13, wherein the logical control channel resources comprise a number of logical resources that may vary between a minimum and a maximum and wherein the scheduler is configured to select a number of logical resources for control channel resources.
 19. The method apparatus of claim 18, wherein the scheduler is configured to release any logical resources between the maximum and the number of selected logical resources for assignment to traffic channels.
 20. An apparatus for generating control channel messages in a wireless communication system, the apparatus comprising: means for assigning logical control channel resources to physical channel resources to generate assigned physical channel resources, wherein the logical control channel resources are distinct from logical traffic channel resources assigned for data transmission and the physical channel resources correspond to combinations of sub-carriers and OFDM symbols; means for generating at least one message; means encoding the at least one message to generate at least one message symbol; and a transmitter configured to transmit the at least one message on at least a portion of the assigned physical channel resources.
 21. The apparatus of claim 19, further comprising means for controlling a power density of the at least one message.
 22. The apparatus of claim 20, wherein the means for assigning comprises means for assigning based in part on a frequency hopping algorithm.
 23. The apparatus of claim 20 wherein the logical control channel resources comprise nodes of a channel tree and the means for assigning comprises means for mapping the nodes to a sub-carriers and OFDM symbols.
 24. The apparatus of claim 23, wherein the means for mapping comprises means for mapping the nodes based in part on a frequency hopping algorithm.
 25. The apparatus of claim 20, wherein the logical control channel resources comprise a number of logical resources that may vary between a minimum and a maximum and wherein the means for assigning comprises means for selecting a number of logical resources for control channel resources. 